Muffle furnace with sighting assembly

ABSTRACT

A vacuum furnace is provided embodying means operable for improving the ability of one to visually inspect work undergoing heating while under vacuum. The vacuum furnace includes a vacuum chamber and a muffle furnace housed therewithin. The muffle furnace includes a muffle chamber adapted for receiving a work object in supporting relation therewithin upon which some form of work operation involving the use of heat is to be performed. Access to the muffle chamber is provided through a muffle door which is suitably mounted at one end of the muffle furnace for movement between an open and a closed position relative to the aforementioned one end of the muffle furnace. To facilitate the location of a desired field of vision into the interior of the muffle chamber of the muffle furnace, the vacuum furnace is provided with improved visual sighting means. The latter means includes a transparent or translucent window which is suitably provided in the muffle door wherein to be operable to enable one to see into the muffle chamber. Aligned with but spaced from the window in the muffle door is a viewing port provided in the vacuum chamber door. The latter door has an open and a closed position and is operable to provide access therethrough to the muffle door of the muffle furnace and thereby to the interior of the muffle chamber. For purposes of opening the door of the vacuum chamber, a handle is provided in which an annular ring comprising a sighting hole is suitably located so as to be visually aligned with the viewing port in the vacuum chamber. The latter viewing port in turn is visually alignable with the window in the muffle door when the muffle furnace door and the vacuum chamber door are in their closed positions whereby the aforedescribed three sighting means function to provide a desired field of vision into the interior of the muffle furnace chamber.

United States Patent 1191 Winslow 14 1 Jan. 7, 1975 MUFFLE FURNACE WITH SIGHTING ASSEMBLY Donald L. Winslow, Lake Arrowhead, Calif.

[73] Assignee: The J. M. Ney Company,

Bloomfield, Conn.

22 Filed: Jan. 21, 1974 211 Appl. No: 434,815

[75] Inventor:

Primary ExaminerJohn J. Camby [57] ABSTRACT A vacuum furnace is provided embodying means operable for improving the ability of one to visually inspect work undergoing heating while under vacuum. The vacuum furnace includes a vacuum chamber and a muffle furnace housed therewithin. The muffle furnace includes a muffle chamber adapted for receiving a work object in supporting relation therewithin upon which some form of work operation involving the use of heat is to be performed. Access to the muffle chamber is provided through a muffle door which is suitably mounted at one end of the muffle furnace for movement between an open and a closed position relative to the aforementioned one end of the muffle furnace. To facilitate the location of a desired field of vision into the interior of the muffle chamber of the muffle furnace, the vacuum furnace is provided with improved visual sighting means. The latter means includes a transparent or translucent window which is suitably provided in the muffle door wherein to be op erable to enable one to see into the muffle chamber. Aligned with but spaced from the window in the muffle door is a viewing port provided in the vacuum chamber door. The latter door has an open and a closed position and is operable to provide access therethrough to the muffle door of the muffle furnace and thereby to the interior of the muffle chamber. For purposes of opening the door of the vacuum chamber, a handle is provided in which an annular ring comprising a sighting hole is suitably located so as to be visually aligned with the viewing port in the vacuum chamber. The latter viewing port in turn is visually alignable with the window in the muffle door when the muffle furnace door and the vacuum chamber door are in their closed positions whereby the aforedescribed three sighting means function to provide a desired field of vision into the interior of the muffle furnace chamber.

8 Claims, 5 Drawing Figures FMENTED JAN 7 5 SHEEI 10F 2 MUFFLE FURNACE WITH SIGHTING ASSEMBLY BACKGROUND OF THE INVENTION During the process of manufacturing many different forms of products, there is a need to perform on the product some type of work operation requiring the application of heat. Moreover, some of these work operations involve the use of heat at elevated temperature. Most commonly, the application to the product of heat at elevated temperatures is done while the product is supported within an enclosed structure. More particularly, a furnace in which the product is positioned is conventionally employed for this purpose both because it constitutes a means possessing the capability of enabling the necessary elevated temperatures to be achieved therewithin as well as because of safety considerations.

As is readily apparent from even a cursory reference to the state of the art, there have long been provided furnaces embodying one form of construction or another which have been designed primarily for use in industrial applications for heating a product. Commonly, these furnaces have been designed basically for use in connection with particular forms of products and/or to enable particular types of work operations to be performed through the use thereof. Consequently, there can be found in the prior art, industrial furnaces of varying sizes and shapes, and which are operable to provide heat at varying ranges of temperature to the interior of the chamber formed therewithin. Moreover, there have been provided heretofore furnaces which are designed to be operable in different environments. In this connection for example, it has been known heretofore to provide a furnace which is designed to function in a vacuum atmosphere whereby heating of the product is accomplished while the latter is under a vacuum.

all sizes and shapes have been provided heretofore, one undesirable feature which most often is found to characterize prior art forms of furnaces is the fact that it is difficult to observe a product while it is being heated therein. Although some types of work operations may not require that the product be observed during heating, there are many applications in which there is a need to observe within the furnace. More particularly, in this connection reference is had to the need to make observations of such things as for example, solder or braze flow temperature, fusion temperature or porcelain glazing temperature. Commonly, to satisfy this need to make observations, some form of window has been provided in the door of the furnace. Moreover, in this regard some manufacturers have even gone as far as to market specially designed doors embodying viewing means therein. The latter doors are designed to be substituted for the original doors with which the furnaces were provided.

Nevertheless, however, it has been found that when an attempt is made to see into the furnace through such prior art forms of viewing means that it is difficult to locate the object therewithin and/or the particular area of the object which is of interest. This is because of the fact that a lack of color contrast commonly exists between objects which are at the same temperature. More specifically, the difficulty in making observations stems in large part from the fact that the aforereferenced Notwithstanding the fact that a variety of furnaces of prior art forms of viewing means fail to embody means operable to focus the field of vision to a particular location within the furnace whereat the product needing to be observed may be positioned. Attempting to observe a product located within a furnace under the aforedescribed circumstances is made even more difficult in the case for example, of a vacuum furnace wherein the work, i.e., product to be observed is located within an enclosed furnace which itself is in turn positioned within another closed chamber.

There has therefore existed a need to provide a furnace with visual sighting means operable for improving the ability of one to visually inspect work undergoing heating in a furnace by causing the field of vision pro vided therethrough to be focused to a particular por tion of the interior of the furnace whereat the work is to be found located. Moreover, a need has existed to provide such a visual sighting means which is capable of being embodied in a wide variety of furnaces of all different types, shapes and sizes. In this connection also, a need has existed to provide such a visual sighting means specifically capable of being employed in a vacuum furnace to facilitate location of a desired field of vision within a furnace which is itself located in a vacuum chamber whereby to enable some one positioned at the exterior of the vacuum chamber to observe an object being heated under a vacuum in the furnace located within the vacuum chamber.

Accordingly, it is an object of the present invention to provide a novel and improved visual sighting means for a furnace operable to improve the ability of one to visually inspect work undergoing heating in the furnace.

It is another object of the present invention to provide such a visual sighting means for a furnace which is operable to cause the field of vision into the furnace to be focused to a particular location within the interior of the furnace whereat the work is capable of being positioned while undergoing heating.

Another object of the present invention is to provide such a visual sighting means for furnaces which is char acterized by its universality in that it is capable of being utilized in a wide variety of furnaces of different types, sizes and shapes.

A still further object of the present invention is to provide such a visual sighting means for a furnace which is operable to facilitate locating a desired field of vision into the furnace while at the same time not constituting a source of loss of heat therethrough from within the furnace to the exterior thereof.

Yet another object of the present invention is to provide such a visual sighting means for a furnace which is specifically capable of being employed in a vacuum furnace to facilitate location of a desired field of vision into a furnace which is in turn positioned within a vacuum chamber to enable one to visually inspect work being heated under a vacuum.

SUMMARY OF THE INVENTION It has now been found that the foregoing and related objects can be readily attained in a furnace embodying a novel and improved visual sighting means operable for improving the ability of one to visually inspect work while the latter is undergoing heating within the furnace. The furnace includes a chamber adapted for receiving a work object in supporting relation therewithin upon which some form of work operation involving the use of heat is to be performed. Access to the chamber is provided through a door which is suitably mounted at one end of the furnace for movement between an open and a closed position relative to the aforesaid one end of the furnace. To facilitate the location of a desired field of view into the chamber of the furnace, the latter is provided with the aforereferenced improved visual sighting means. The visual sighting means includes a window which is provided in the door and which functions as a port for viewing into the interior of the chamber in the furnace. The visual sighting means also includes a sighting hole. Means are provided on the furnace operable for supporting an annular ring comprising the sighting hole which is alignable with but spaced from the window in the door of the furnace. The sighting hole is suitably positioned so as to be located in aligned relation with the window in the door of the furnace when the latter door is in its closed position. The sighting hole and the window in the door when aligned cooperate to cause the field of vision provided thereby to be focused to a particular area within the chamber of the furnace whereby a work object positioned thereat may be observed from the exterior of the furnace while undergoing heating therewithin.

In accord with the preferred form of the invention, the visual sighting means is embodied in a vacuum furnace. The vacuum furnace includes a vacuum chamber and a muffle furnace which is housed within the vacuum chamber. The muffle furnace includes the chamber in which the work is positioned for heating. To permit the work to be inserted into the muffle furnace chamber the muffle furnace has a suitably mounted door provided at one end thereof movable between an open and a closed position relative to the housing of the furnace. A transparent or translucent window is suitably provided in the muffle door which is operable for purposes of enabling one to see therethrough into the interior of the muffle chamber. Aligned with but spaced from the window in the muffle door is a viewing port which is provided in the door of the vacuum chamber in which the muffle furnace is located. The vacuum chamber door has an open and a closed position and is operable to provide access therethrough to the muffle door of the muffle furnace and thereby to the interior of the muffle chamber. For purposes of opening the door of the vacuum chamber, a handle is provided suitably supported thereon. The handle is provided with an annular ring which functions as a sighting hole. The sighting hole is suitably located on the handle so as to be visually aligned with the viewing port provided in the door of the vacuum chamber. The latter viewing port in turn is visually alignable with the window in the muffle door when the muffle furnace door and the vacuum furnace door are in their closed positions whereby the aforedescribed three sighting means function to provide a desired field of view into the interior of the muffle furnace chamber.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded view of a visual sighting means constructed in accordance with the present invention, illustrated embodied in a furnace;

FIG. 2 is a front view of a furnace embodying a visual sighting means constructed in accordance with the present invention;

FIG. 3 is a cross-sectional view of a visual sighting means for a furnace constructed in accordance with the present invention, illustrated embodied in a furnace with the latter being depicted therein in phantom lines;

FIG. 4 is a top plan view of the handle and door as sembly of a vacuum furnace provided with a visual sighting means constructed in accordance with the present invention; and

FIG. 5 is a cross-sectional view of a portion of the handle and door assembly of the vacuum furnace of FIG. 4, illustrated with parts broken away in the interest of maintaining clarity of illustration and depicting the manner in which the handle is attached to the door.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring now to the drawings and more particularly FIGS. 1 and 3 thereof, there is illustrated therein a vacuum furnace, generally designated by reference numeral l0, embodying a vacuum sighting means, generally designated by reference numeral 12, constructed in accordance with the present invention. The vacuum furnace 10 includes a vacuum chamber 14 and a muffle furnace 16, the latter being housed within the vacuum chamber 14.

As best understood with reference to FIG. I of the drawings, the muffle furnace 16 in a manner wellknown to those skilled in the art has a construction which includes a substantially closed cylindrically shaped housing 18 having a chamber 20 formed at the interior thereof. At one end thereof, the muffle furnace 16 is provided with an opening 22 affording access to the interior of the muffle furnace 16 and more particularly to the chamber 20 formed therein. The latter chamber 20 is suitably configured so as to be adapted to receive work in supported relation therewithin upon which it is desired to perform some type of work ope ra tion involving the application of heat to the work. For purposes of enabling the opening 20 to be closed, the muffle furnace 16 is provided with a door 24. The latter door 24 is cooperatively associated through the use of any conventional form of mounting means with the housing 18 of the muffle furnace 16 whereby to enable the door 24 to occupy an openand a closed position relative to the opening 22 formed in one end wall of the muffle furnace 16. In this connection, the door 24 may be constructed so as to be completely removable from the opening 22 as suggested in the illustration thereof found in FIG. 1 of the drawings. In accord with the latter form of construction, the door 24 as illustrated in FIG. 3 of the drawings has a generally L-shaped configuration having a leg portion 24a which is insertable into the opening 22 formed in the aforementioned one end wall of the muffle furnace l6 and with the other leg portion 24b thereof extending at right angles to the major axis of the muffle furnace l6 and being positioned in abutting engagement with the front face of the muffle furnace 16. It will further be noted with reference to FIG. 3 of the drawings that the novel furnace door 24 possesses a considerable thickness, the latter being operable to minimize the possibility of any significant amount of heat being lost therethrough from the interior to the exterior of the novel furnace I6.

Completing the description of thenature of the construction of the muffle furnace 16, the latter is preferably provided as illustrated in FIGS. 1 and 3 of the drawings with a support member 26 having a generally L shaped configuration. The member 26 is mounted on the exterior of the muffle furnace 16 through the use of any suitable conventional form of mounting means (not shown). More particularly, the leg portion 26a of member 26 is affixed to the housing 18 of the muffle furnace 16 with the other leg portion thereof, i.e., leg portion 26b of the member 26 extending outwardly away from the housing 18 of the muffle furnace 16. In addition, it will be noted that the support member 26 is suitably located relative to the opening 22 in the muffle furnace 16 so that the leg portion 26b of the member 26 lies substantially in the same plane as the bottom surface of the opening 22. As depicted in FIG. 3 of the drawings, with the door 24 occupying its closed position relative to the opening 22, the support member 26 is operable to provide a rest for the door 24. Finally, although not shown in the drawings inasmuch as the construction and mode of operation thereof are wellknown to those skilled in the art and inasmuch as it is only indirectly related to the subject matter of the present invention, it is nevertheless to be understood that the muffle furnace l6 embodies therein suitable conventional heating means operable for providing heat at elevated temperatures within the chamber 20 of the muffle furnace 16 whereby to cause work located within the chamber 20 to become heated.

Turning next to a consideration of the nature of the construction of the vacuum chamber 14, the latter may take the form of any of the various types of such chambers presently commercially available which are designed for use with muffle furnaces. Basically, however, the vacuum chamber 14 includes a housing 28 having one end thereof open whereby to provide a means to enable access to be had to the interior of the vacuum chamber 14. The vacuum chamber 14 in addition is provided with a door 30 which is operable for purposes of closing off the open end of the housing 22. More particularly, the door 30 has an open and a closed position relative to the open end of the housing 28 of the vacuum chamber 14 whereby when the door 30 is in its open position access may be had therethrough to the muffle door 24 and thereby to the interior of the muffle furnace 16, i.e., the chamber 20 thereof to enable work to be positioned within and removed from the muffle furnace chamber 20. Preferably a suitable gasket 32 of conventional construction is interposed between the rim of the open end of the housing 28 of the vacuum chamber 14 and the door 30 thereof whereby when the door 30 is in its closed position a tight seal is provided between the door 30 and the housing 28. Inasmuch as the means with which the vacuum chamber 14 is provided for purposes of enabling a vacuum to be drawn therewithin comprises conventional structure which is well-known to those skilled in the art and inasmuch as such means is only indirectly related to the subject matter of the present invention, it has not been deemed necessary to illustrate such means in the drawings. Rather, it has been deemed sufficient to merely set forth at this point that the vacuum furnace l consisting of the vacuum chamber 14 and the muffle furnace 16 is operable to enable work placed in the chamber 20 of the muffle furnace 16 to be heated while under a vacuum.

To facilitate the opening and closing of the door 30 of the vacuum chamber 14, a handle 34 is preferably provided in supported relation on the door 30. The handle 34 comprises an elongated member having a length substantially equal to the diameter of the door 30 of the vacuum chamber 14 and has a width which is greatest at the midpoint thereof. More particularly, as depicted in the drawings the handle 34 is preferably provided with a configuration wherein the handle 34 is tapered inwardly from the midpoint thereof to the opposite ends 54 and 56 thereof. At the midpoint thereof, the handle 34 has formed therethrough an annular ring 58 which comprises one of the components of the previously referenced visual sighting means 12. The annular ring 58 in a manner which will be described subsequently functions as a sighting hole. Intermediate the ends 54 and 56 thereof, the handle 34 is also provided with a pair of recessed areas 60 and 62. Located behind the surfaces of both of the recessed areas 60 and 62 in a manner yet to be described are means operable for attaching the handle 34 on the door 30. In accord with the illustrated embodiment thereof, the handle 34 is also provided with an arm 64 which is joined to the end 56 of the handle 34 so as to extend substantially at right angles to the principal plane of the handle 34. Adjacent to its free end, the arm 64 as depicted in FIG. 4 of the drawings is provided with an opening 66 formed therethrough which is suitably dimensioned so as to be capable of receiving therein a conventional form of fastening means including a pin 67 receivable in the protuberances 69. Through the employment of such a fasten ing pin 67 positioned within the opening 66 so as to pass therethrough into engagement with the openings provided therefor in the protuberances 69 located on the housing 28 of the vacuum chamber 14, the arm 64 is operable for purposes of mounting the handle 34 and thereby also the door 30 which is attached thereto on the housing 28 of the vacuum chamber 14 so that the handle 34 and the door 30 may swing as a unit relative to the open end of the vacuum chamber 14 between a first position wherein the door 30 is located in spaced relation to the open end of the housing 28 which corre sponds to the open position of the door 30 and a second position wherein the door 30 and more particularly the gasket 32 supported thereon is in abutting engagement with the rim of the housing 28 defining the open end wall thereof which corresponds to the closed position of the door 30.

Turning now to FIG. 5 of the drawings, the handle 34 is attached to the door 30 at two points. inasmuch as the means by which the handle 34 and the door 30 are joined together at each of the two points are identical, a description will be set forth hereinafter of only one of these means with it being understood that the structure of the other is substantially identical. in this connection, as depicted in FIG. 5, the handle 34 is provided with a recessed area 68 which is alignable with an opening, i.e., recessed area 70 formed in the door 30. ln accord with the illustrated embodiment thereof, the dimensions of the recessed area 68 are greater than those of the recessed area 70. The interconnection between the handle 34 and the door 30 is accomplished by means of a threaded fastener 72. The latter fastener 72 is positioned in the aforereferenced recessed areas 68 and 70 with the head portion thereof received in the recessed area 68 formed therefor in the handle 34 and with the threaded end portion thereof received in the opening 70 formed therefor in the door 30. lntermedi ate the ends thereof the threaded fasteners 72 preferably has positioned thereon a nut 74. The latter is provided for purposes of functioning as a stop means whereby to limit the extent of relative movement which is possible between the handle 34 and the door 30. In

this connection, it will be noted with reference to FIG. of the drawings that the circumference of the nut 74 is greater than the recessed area, i.e., opening 70 formed in the door 30 and the opening which extends the remainder of the way through the handle 34 from the recessed area 68 thereof. In addition, as depicted in FIG. 5 of the drawings, a spring 76 surrounds the threaded fastener 72 and the nut 74 provided thereon with one end of the spring 76 bearing against the door 30 and the other end of the spring 76 bearing against the handle 34. It can readily be understood therefore that the spring 76 is operable to apply a biasing force against both the door 30 and the handle 34 and thereby functions to bias the latter two components apart. In

order to ensure that the head portion of the threaded fastener 72 remains positioned in the recessed area 68 of the handle 34, a C-shaped washer 78 is preferably positioned on the head portion of the threaded fastener 72 in an annular groove (not shown) formed therein for this purpose. Finally, in accord with the illustrated embodiment of the vacuum furnace 10, a member 80 is preferably positioned over the recessed area 68 formed in the handle 34 wherein it is operable to provide a cover for the various elements including the threaded fastener 72, etc., which constitute the means by which the door 30 and handle 34 are attached together.

Referring now to the structure embodied in the visual sighting means 12, the latter consists of three sighting means, which cooperate together to cause the field of vision of some one located at the exterior of the vacuum furnace 10 looking therein, to be focused to a particular area within the chamber of the muffle furnace 16 whereat the work which is to be heated therein may be located thereby to ensure that the work and/or a particular portion of the work is capable of being visually inspected from the exterior of the vacuum furnace 10 while the work is being heated under a vacuum. The visual sighting means 12 includes a window 36 mounted in the door 24 of the muffle furnace 16, a viewing port 42 provided in the door of the vacuum chamber 14, and the annular ring 58 which functions as a sighting hole that is formed in the handle 34. Considering first the window 36, to mount the latter in the door 24 the window 36 is inserted through the slot 38 formed in the leg portion 24b of the door 24 so that the window 36 occupies a position wherein it traverses the opening 40 formed through the door 24. As shown in FIG. 3 of the drawings, when mounted in the door 24 the window 36 lies in the plane of the leg portion 24b and perpendicular to the plane of the leg portion 24a of the door 24. The window 36 may be formed of any suitable transparent or translucent material capable of withstanding the elevated temperatures which are caused to occur in the chamber 20 of the muffle furnace 16. In this connection, quartz has been found to be suitable for such a use.

With reference next to the nature of the viewing port 42, the latter preferably comprises a polygonal-shaped member formed of a suitable transparent or translucent material. As best understood with reference to FIG. 3 of the drawings, the viewing port 42 is mounted in a cutout portion 44 located substantially at the center of the door 30 of the vacuum chamber 14 and so as to be substantially equally distantly spaced from the front and rear surfaces of the door 30. More particularly, the door 30 is provided with a through opening having differing dimensions. Namely, as seen with reference to FIG. 3, the portion of the opening extending inwardly from the rear face, i.e., the right face as viewed with reference to FIG. 3 of the door 30 is smaller than the portion 52 of the opening extending inwardly from the front, i.e., left face of the door 30. To mount the viewing port 42 in the aforedescribed portion 44 in door 30, the viewing port 42 is inserted through the portion 52 of the opening, the latter being suitably dimensioned to make this possible, into engagement with a gasket-like member 46, the latter having first been positioned in the cutout portion 44 so as to lie adjacent to the portion 50 of the through opening in the door 30. After the viewing port 42 has been inserted in the cutout portion 44, a second gasket-like member 48 is preferably also inserted therein so as to be positioned in engagement with but on the other side of the viewing port 42 whereby to effectively cause the viewing port 42 to be held captive between the two gasket-like members 46 and 48. The latter members 46 and 48 may be formed of any suitable resilient material capable of withstanding the environmental conditions which are commonly found to be present in vacuum furnaces. Finally, as best understood with reference to FIG. 3 of the drawings, with the viewing port 42 so mounted in the door 30 of the vacuum chamber 14, andthe window 36 mounted in the previously described manner in the door 24 of the muffle furnace 16, the viewing port 42 is aligned with the window 36 when the muffle furnace door 24 and the vacuum chamber door 30 are in their closed positions.

Finally, insofar as concerns the annular ring 58, the latter as described previously is located substantially at the center of the handle 34 whereby when the door 30 of the vacuum chamber 14 and the handle 34 are attached together, the annular ring 58 is aligned with the viewing port 42 provided in the door 30. Moreover, by virtue of the existence of the spring 76 and the nut 74 which are positioned on each of the threaded fasteners 72, the annular ring 58 is held in spaced relation relative to the viewing port 42. In addition, as best understood with reference to FIG. 3 of the drawings, the side walls which define the annular ring 58 taper inwardly from the front, i.e., left face of the handle 34 as viewed with reference to FIG. 3 of the drawings to the rear, i.e., right face thereof. Because of this taper, the field of vision of one looking through the sighting hole 58 is caused to converge towards a point as has been attempted to be schematically depicted in FIG. 3 of the drawings through the use of the pair of converging broken lines between which the words FIELD OF Vl- SION appear.

Turning now to a description of the manner in which the vacuum furnace l0 embodying the visual sighting means 12 operates, with the vacuum chamber door 30 and the muffle furnace door 24 both in their open positions, work to be heated under a vacuum is inserted into the muffle furnace chamber 20 through the aforedescribed open doors. More particularly, the work is positioned therewithin at the location whereat the field of view of one looking through the sighting hole 58 in the handle 34 is focused. The latter location may if so desired be marked through the use of suitable identifying means (not shown) operable to facilitate the identification of the area in the muffle chamber 20 whereat the work is to be positioned. With the work so supported within the muffle chamber 20, the muffle furnace door 24 is placed in its closed position. Thereaf ter, the vacuum chamber door 30 is closed by swinging the latter by means of the handle 34 attached thereto about the pin 67. Heat is then caused to be applied to the work while the vacuum is drawn in the vacuum chamber 14. While the work is being heated, the latter may be visually inspected by means of the visual sight ing means 12. To this end, in the manner described hereinabove, by virtue of the tapered side walls of the sighting hole 58 and the alignment of the latter with the viewing port 42 and the window 36 when the vacuum chamber door 30 and the muffle furnace door 24 are in their closed positions, the field of vision of one peering therethrough is necessarily caused to converge to a desired location within the muffle furnace chamber 20 whereat the work may be positioned for heating. The work when so located remains readily visible notwithstanding the fact that a lack of color contrast may exist between the work and the interior of the muffle chamber 20 and/or other objects positioned in the latter. Obviously, visual sighting means 12 is also operable for purposes of making observations such as for example, of solder or braze flow temperature, fusion temperature or porcelain glazing temperature.

Although only one embdiment of a visual sighting means for a furnace constructed in accordance with the present invention has been shown in the drawings and described hereinabove, it is to be understood that modifications in the construction thereof may be made thereto by those skilled in the art without departing from the essence of the invention. In this connection, some of the modifications which can be made in the visual sighting means for a furnace have been alluded to hereinabove while others will become readily apparent to those skilled in the art when exposed to the present description and illustration of the construction of the visual sighting means 12. For example, although the components which comprise the visual sighting means 12, namely the window 36, viewing port 42 and sighting hole 58 have been described hereinabove and illustrated in the drawings as being embodied in a particular form of muffle furnace 16 and vacuum chamber 14, it is to be understood that the visual sighting means 12 is also capable of being utilized in vacuum furnaces wherein the vacuum chamber and the muffle furnace thereof embody other forms of construction. Moreover, the window 36 may be mounted within the door of the muffle furnace in some other manner from that described hereinabove without departing from the essence of the invention. Similarly, the viewing port 42 and the sighting hole 58 may be provided in the vacuum chamber door 30 and the handle 34, respectively, in some other manner without departing from the essence of the invention. More particularly, the latter modifications involving the mounting of the window 36, viewing port 42 and the sighting hole 58 may be made without departing from the essence of the invention as long as all of these elements are capable of being aligned relative to each other when the door of the muffle furnace and the door of the vacuum chamber are in their closed positions. Finally, although the visual sighting means of the present invention has been described and illustrated as being embodied in a vacuum furnace 10, it is to be understood that the visual sighting means of the present invention may also be employed in other types of furnaces. In this connection, in some applications wherein work is to be heated without being under a vacuum and accordingly there is no requirement that the furnace be positioned within a vacuum chamber, the door of the furnace in the latter instance may embody the type of construction possessed by the door 30 of the vacuum chamber 14, i.e., the door of the furnace may be provided with a window which is similar in construction to the viewing port 42 and the door may also have means supported thereon provided with a sighting hole which is aligned with but spaced from the aforementioned window in the door.

Thus, it can be seen that the present invention pro vides a novel and improved visual sighting means for a furnace operable to improve the ability of one to visually inspect work undergoing heating in the furnace. Moreover, in accord with the present invention a visual sighting means for a furnace is provided which is operable to cause the field of vision into the furnace to be focused to a particular location within the interior of the furnace whereat the work is capable of being positioned while undergoing heating. The visual sighting means for furnaces of the present invention is characterized by its universality in that it is capable of being utilized in a wide variety of furnaces of different types, sizes and shapes. Also, in accordance with the present invention a visual sighting means for a furnace is provided which is operable to facilitate locating a desired field of view into the furnace while at the same time not being a source of heat loss from within the furnace to the exterior thereof. Finally, the visual sighting means for a furnace in accord with the present invention is specifically capable of being employed in a vacuum furnace to facilitate location of a field of vision into a furnace which itself is positioned within a vacuum chamber to enable one to visually inspect work being heated under a vacuum.

Having thus described the invention, I claim:

1. In a muffle furnace with viewing means operable for viewing into the interior of the furnace, the combination comprising:

a. a support;

b. a muffle on said support and having a chamber therein and an opening in one wall thereof affording access to said chamber, said muffle including a door having an opening therethrough and supported on said muffle to close said opening therein, and said door including transparent window means traversing said opening therein operable for viewing said chamber of said muffle; and

0. viewing means separately supported on said support in outwardly spaced relationship to said door in alignment with said window means, said viewing means including a transparent window port larger in cross sectional area than said window means, said viewing means and window means when aligned with said door in said muffle closing position being operable to cause the field of vision of a user outwardly of said viewing means to converge so as to focus at a location within said chamber.

2. In a muffle furnace, the combination as set forth in claim 1 wherein said support comprises a housing for 5. In a muffle furnace, the combination as set forth and in claim 4 wherein said housing further includes a hanc. viewing means supported on said door of said dle attached to said door and said viewing means furhousing traversing said opening in said door of said ther includes 3. sighting hole formed in said handle in housing for viewing within aid housing aid iewaligned but spaced relation to said viewing port formed 5 m means including a transparent window port in said door of said housing. 6. A vacuum furnace with viewing means operabl for viewing within the interior of the furnace comprising:

a. a housing having an opening in one wall thereof,

said housing including a door having an opening therein and supported on said housing to close said of a user outwardly f saldhQusmg to converge so Opening therein; as to focus at a location within said chamber.

a muffle Separately Supported in Said housing and 7. The vacuum furnace as set forth in claim 6 wherein having a chamber therein and an opening in one said housing 18 operable as a vacuum chamber. wail th f ff di access to Said chamber, Said 8. The vacuum furnace as set forth In claim 6 further muffle including a door having an opening therecomPrlsmg a hafidle PPQ Said door through and supported on said muffle to close said Q g and .havmg a slghtmg hole formedfhefem i opening therein, and said door including transparaligned relation but spaced from said opening in said ent window means traversing said opening therein 2() door of said housing. operable for viewing said chamber of said muffle;

larger in cross sectional area than said window means, said viewing means and window means when aligned with said housing door in said closing position and said muffle door in said muffle closing position being operable to cause the field of vision 

1. In a muffle furnace with viewing means operable for viewing into the interior of the furnace, the combination comprising: a. a support; b. a muffle on said support and having a chamber therein and an opening in one wall thereof affording access to said chamber, said muffle including a door having an opening therethrough and supported on said mUffle to close said opening therein, and said door including transparent window means traversing said opening therein operable for viewing said chamber of said muffle; and c. viewing means separately supported on said support in outwardly spaced relationship to said door in alignment with said window means, said viewing means including a transparent window port larger in cross sectional area than said window means, said viewing means and window means when aligned with said door in said muffle closing position being operable to cause the field of vision of a user outwardly of said viewing means to converge so as to focus at a location within said chamber.
 2. In a muffle furnace, the combination as set forth in claim 1 wherein said support comprises a housing for said muffle.
 3. In a muffle furnace, the combination as set forth in claim 2 wherein said housing includes a door and said viewing means is supported on said door of said housing.
 4. In a muffle furnace, the combination as set forth in claim 3 wherein said viewing means has said viewing port formed in said door of said housing.
 5. In a muffle furnace, the combination as set forth in claim 4 wherein said housing further includes a handle attached to said door and said viewing means further includes a sighting hole formed in said handle in aligned but spaced relation to said viewing port formed in said door of said housing.
 6. A vacuum furnace with viewing means operable for viewing within the interior of the furnace comprising: a. a housing having an opening in one wall thereof, said housing including a door having an opening therein and supported on said housing to close said opening therein; b. a muffle separately supported in said housing and having a chamber therein and an opening in one wall thereof affording access to said chamber, said muffle including a door having an opening therethrough and supported on said muffle to close said opening therein, and said door including transparent window means traversing said opening therein operable for viewing said chamber of said muffle; and c. viewing means supported on said door of said housing traversing said opening in said door of said housing for viewing within said housing, said viewing means including a transparent window port larger in cross sectional area than said window means, said viewing means and window means when aligned with said housing door in said closing position and said muffle door in said muffle closing position being operable to cause the field of vision of a user outwardly of said housing to converge so as to focus at a location within said chamber.
 7. The vacuum furnace as set forth in claim 6 wherein said housing is operable as a vacuum chamber.
 8. The vacuum furnace as set forth in claim 6 further comprising a handle supported on said door of said housing and having a sighting hole formed therein in aligned relation but spaced from said opening in said door of said housing. 